The background description provided herein is for the purpose of generally presenting the context of the present invention. The subject matter discussed in the background of the invention section should not be assumed to be prior art merely as a result of its mention in the background of the invention section. Similarly, a problem mentioned in the background of the invention section or associated with the subject matter of the background of the invention section should not be assumed to have been previously recognized in the prior art. The subject matter in the background of the invention section merely represents different approaches, which in and of themselves may also be inventions.
Physiological vital signs, for example, the body temperature (BT), the heart rate (HR), and/or the respiration rate (RR), along with the quantitative features extracted from these vital signs, such as heart rate variability (HRV) that measures the variation of beat-to-beat time interval, are direct indicators of a person's physical and psychological state and wellness. Therefore, persistent monitoring of vital signs prevails in clinic, gym and home settings for healthcare, fitness and leisure purposes.
Photoplethysmography (PPG) refers to the optical technique that measures the volumetric changes of an organ or body part. It utilizes the minute variation of light absorption of certain surface or volumetric region of interest (ROI) during physiological activities such as heart beating or breathing. PPG is often obtained by a pulse oximeter which records the time-lapsed change of light reflected from or transmitted through one or more ROI. This time-varying light absorption picked up by a pulse oximeter is a function of changes in arterial blood oxygen saturation and changes in blood volume in the skin.
Typically, a pulse oximeter comprises a red light emitting diode (LED) and an infrared LED as an illumination unit and a photodetector as a light sensing unit. Under the most common transmissive operation mode, the illumination unit contacts one side of a thin part of a living subject's body, such as a fingertip, earlobe, or forehead, emitting two wavelengths of light that are picked up by the light sensing unit from the other side. The illumination unit quickly switches between shots of red and infrared light, allowing the photodetector to measure the changing absorbance at each wavelength. Subsequent analysis of such dual-wavelength measurement (time division multiplexing) reveals the absorbance due to the arterial blood alone, removing artefacts from venous (deoxygenated) blood, skin, bone, muscle, fat, etc.
Although PPG is a favorable means of gauging vital signs as being simple, low-cost, and non-invasive, its nature of requiring direct contact between the PPG system and the living subject's body may lead to unpleasant and obtrusive experience. To ensure a good sensor attachment, most commercially available pulse oximeters are clamped onto fingertips or earlobes, exerting a pressure over the living subject's tissue that could cause discomfort. In addition, the PPG system and any attached cable would also prevent the subject from performing certain movement or work.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.